Magnon auto-oscillation under zero magnetic field

Magnons are attractive for application in energy efficient information technology, because they propagate without any actual charge currents and they offer high frequencies up to THz range. Here we present a novel scheme for magnon generation using spin currents and domain walls.
When a charge current is applied to a heavy metallic/ferromagnetic bilayer, the spin currents originating from a spin Hall effect in the heavy metal apply a spin transfer torque on the magnetization. This allows driving efficiently auto-oscillations of magnetization [1]. We focused on domain walls as local magnon nano channels [2]. Since domain walls can be moved by electrical currents [3], they are attractive for reprogrammable nano circuits.
A 370 nm wide zigzag structure was fabricated from a Pt/CoFeB bilayer. A domain wall was generated at the apex by magnetic saturation. The magnon intensity on the remanent state was measured by Brillouin light scattering microscopy [4] with applying a dc current. The magnon excitation showed the dc current dependency. Magnons were detected only for positive dc currents. We succeeded to drive magnon auto-oscillation in the domain wall under zero magnetic field by spin transfer torque.

Reference
[1] A. N. Slavin and V. Tiberkevich, IEEE Trans. Magn. 45, 1875 (2009).
[2] K. Wagner et. al., Nat. Nanotech. 11, 432 (2016).
[3] S. S. P. Parkin et. al., Science 320, 190 (2008).
[4] T. Sebastian et. al., Front. Phys. 3, 35 (2015).